Mooring buoy assembly



Sept 10, 1963 H. B. BOLTON 3,103,020

MOORING BUOY ASSEMBLY Filed sept. 15, 19Go 34 M.H.H.w.

MEAN sEALEvEL M.l .x .w. -4

mllnl Hum United States Patent O 3,103,020 MUORlNG BUY ASSEMBLY Harold B. Bolton, San Rafael, Calif., assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware Filed Sept. 13, 196i?, Ser. No. 55,652 7 Claims. (Cl. 9-3) This invention relates to mooring buoys, yand more particularly to a mooring buoy assembly which has improved performance characteristics and which functions lat yan offshore location for an extended period of time lwithout frequent maintenance.

A mooring buoy, yas is well understood in the tart, comprises `a buoy or iloat member which is anchored at an offshore location by a slack anchor chain attached to Ia heavy bottom anchor. A vessel is moored by attaching its mooring lines to the oat member. The restraining anchoring force is transmitted from the bottom anchor, through the interconnected yanchor chain to the float member, and thence through the attached mooring lines to the vessel. A-s the vessel exerts increased force on the mooring buoy installation under the inuence of wind ond water `forces at the surface of the water `attempting to move the vessel from its moored position, the float member is pulled downwardly into the water. The resistant -force this member exerts on the vessel increases, tending to restore the vessel to its initial position, and assisting the bottom anchor in restraining the vessel.

In situations where it is desired to restrict the transverse and longitudinal movement of the vessel to a very limited area, such las occurs, for instance, in offshore loading and unloading terminals for oil tankers, mooring stations are established wherein several mooring buoys are :displaced -around the area in which the vessel is to be maintained. The vessel is maneuvered into position in a particular location within the surrounding buoys and secured to them by bow and stern mooring lines, and in some cases by mooring lines placed lamidships of the vessel. All of the buoys then act on the vessel to maintain it in the desired position' where the vappropriate hoses can be connected to .it without danger of rupture while the cargo is being loaded or unloaded.

Mooring buoy stations commonly `are installed in openwater locations where the buoys are exposed to constantly applied wave forces :as well as tidal variations in the elevation of the surface of the water. These forces cause the buoy to be in constant movement, and its elevation above the underwater bottom changes continuously. This movement is transmitted to the lanchor chain which secures it to the bottom anchor. The `constant abrasive wear on the anchor chain, which results from such movement, added to the well-known corrosive effects of a salt-water environment, reduces the useful life of the anchor chain to -a marked degree, particularly in the dip section of the chain adjacent the ocean floor, where the chain curves from the vertical to a horizontal direction. lt is Igood practice, at a well-maintained offshore terminal, to pull the mooring buoys out of the water `and inspect the anchor chains at least once each year, since experience has proved that normally at least some of the anchor chain links must be replaced in this period of time. With equipment of the size used to moor oil tankers, the cost of maintaining the oiishore terminal can be very appreciable and may approximate $10,000 per year for the maintenance of the buoys.

It is among the objects of this invention to provide a novel mooring buoy assemblage which functions in a manner to extend its useful life beyond that of the mooring buoy installations now commonly in use, which will require less frequent maintenance While assuring that the 311,103,020 Patented Sept. 10, 1963 ICC elements of the assemblage are in safe working condition, which will increase the ease with which a vessel can be moored to `an olshore terminal, and which will maintain the moored vessel in position with less periodic increased strain in the |anchor lines due to the rolling iand pitching of the vessel than is presently experienced with existing mooring buoys.

Other objects of this invention will become apparent as the description of it proceeds in conjunction with the accompanying drawings which form part of the specication and in which:

FIG. l illustrates in side elevation a mooring buoy assemblage made in accordance .with this invention;

FIG. 2 illustrates in side elevation `and partly in section details of the construction of the buoyant member of this assemblage;

FIG. 3 illustrates in side elevation a portion of a mooring buoy assemblage embodying la modication of this invention.

The illustration of FIG. l represents the mooring buoy installed in a body of Water in :an operating position. A buoyant member 20 is located lat the surface 22 of the body of water 24 and is connected through a rigidly extending element 26 aixed to it and `an .anchor chain 28 to a mass 30 which is seated on the submerged land surface 32. The buoyant member preferably is of cylinydrical form with domed ends 34 and 36 and in its operating position is set with its longitudinal axis Kdisposed in a vertical position in srnooth water. The rigid element 26 preferably, although not necessarily, is a length of thickwalled pipe placed longitudinally through the cylindrical buoyant member in coaxial relationship and is secured at its upper end to the interior wall 38 of the top domed end 34 of the buoyant member. The element 26 passes through the lower domed end 36 of the buoyant member, to which it is rigidly connected in la fluid-tight manner, as by the weld 40, and projects ydownwardly from the buoyant member in coaxial relationship therewith. Strengthening webs, such as are represented by the web 42, are secured between the buoyant member and the projecting element 26 to strengthen and rigidity the structure.

llt will be understood that a particle on the surface of a body of water influenced by wave action will move in a trochoidal or semielliptical orbit with a vertical displacement approximately equal to the total surface Wave height. Within the body of Water, the orbital motion of the particle decreases with increasing depth until at the ocean bottom this motion becomes substantially zero. Preferably the element 26 projects downwardly from the buoyant member 20 a sutlicient ydistance to place the lower end of it at a depth in the water where the transverse forces imposed on it by the orbital movement of the water particles will be negligible. For example, in an installation in I60` feet of Water, the lower end of the element 26 may be located approximately 30 feet below the surface of the water.

The lower end of the element 26 is Weighted with a dense material, as represented by the cement 44, in a sufoient amount to maintain the axis of the assembled element 26 and the buoyant member 20 in a vertical position when this portion of the assemblage is floating lfreely in `the rwater. The weighting in the element 26 assists in stabilizing the assembly under all operating conditions.

The lower end of the element 26 is closed in a fluidrti'ght manner by a iclosure member 46, and to vit is afiixed a connector member 48 to which the length of anchor chain 2S is pivotally connected. The anchor chain 2S extends ydownwardly through the water and is pivotally connected at its lower end through a connector 5'0` to the weighted mass 30 which in its normal operating position engages the submerged land surface 32.

One of the links 52 of the anchor chain, preferably located in a position near the bottom of the chain, is of triangular form, and to 4it is pivotally connected a second length 54 of anchor chain which extends laterally from a position vertically below the buoyant member to a bottom anchor 56 to which it is pivotally connected, as through a linkage y58. This bottom anchor ultimately will supply the anchoring force to hold a moored vessel in position, and may be of any form'found useful -for this purpose.

It is within Vthe concept of this invention that during normal water conditions and a predetermined range of variations of the elevation of the water surface through tidal action, the buoyant member 2i) will be held at a iixed elevation above the underwater bottom and be restrained from following or moving vertically with the changing lelevation of the water surface. To this end, the Weight of the mass 30 is selected to hold the lower portion of the buoyant member submerged in 'the water an amount greater than would occur with the buoyant member detached (from this mass, this condition being established for a predetermined elevation of the 'water surface below the mean sea level. The weight of the mass 310, however, is not suiiicient to hold the buoyant member stationary in elevation 'when the elevation of the water surface exceeds a predetermined amount above the mean sea level.

,It will be appreciated that, as the water level rises with relation to the buoyant member 20, the buoyant :force exerted by the latter on the bottom mass increases. The parts are proportioned to cause the buoyant force of the member to lift the mass 30 oi bottom when the water level reaches the predetermined elevation above mean sea level. When this occurs, the buoyant member 20 will rise and fall with increased and decreased ele- 'vations of the water surface above the predetermined elevation.

As explained heretofore, the effectiveness of a mooring buoy system is due in part to the restoring force of the buoyant member as it tends `to be pulled downwardly into the water through the action of a mooring line from a Vessel connected to it working against the restraining force of the bottom anchor. The restoring force of the buoy is related to the volume of the latter extending above the surface of the water when `the assemblage is in its operating position. Hence, if the buoy of the present invention were restrained by a bottom mass of sufncient weight to permit the buoy to become completely submerged, the restoring force it would generate on a ships anchor line would, under this condition, become negligible. If, on the other hand, the buoyant member should be made of such dimensions as to extend above the surface of the water under all conditions of surface elevation and with suiiicient buoyant capacity in its top portion to produce an appreciable restoring yforce to a vessels mooring line, the physical structure of the buoyant member would become cumbersome and impractical for anchoring a vessel to it in an eiiicient manner.

To prevent these latter diiiiiculties, the elements of the assemblage of the present invention are proportioned to hold the buoyant member stationary in elevation under water conditions which occur during the greater portion of fthe yearly cycles of changing water conditions, but permit the mass 30 to lift oif bottom and the buoyant member 20 to iloat with an appreciable portion of it exposed above the water surface to provide the desired restoring force in the mooring system when the elevation of the water surface exceeds the predetermined upper limit.

In the embodiment of the invention illustrated in FIG. 1, the parts of. the assemblage are proportioned to hold the buoyant member stationary in elevation between the limits of mean lower low water and mean higher high water. Within lthese limits, since the buoyant member will not change elevation as the surface of the Water changes, the amount and frequency of movement in the length of anchor chain 218 will be reduced considerably below that which occurs in the mooring buoy installations now commonly in use. The amount of wear of the anchor chain in the Idip section adjacent the submerged land surface, where it is more exposed to abrasive particles entrained in the water, is proportional to the amount of -movement and rubbing action occurring between the links of the chain. Thus, by reducing the movement of the ichain in this region, the wear of the chain is proportionately reduced, and its useful life is extended.

A vessel is moored to this `assemblage by securing a mooring line from the vessel `to the hook 60 which is pivotally mounted on the top lend portion of the buoyant member 20. The tension of the mooring line is transmitted through the element 26 yto the length of anchor chain 28, thence under conditions 4to be explained hereinafter, through the connecing link 52 =to the second length of anchor chain 54, :and iinally to the `bottom anchor 56. As the force imposed by the vessel ion the mooring system increases, the buoyant member 20l and the element 26 are canted from the vertical to Ibring the parts more nearly into alignment between the vessel andthe bottomengaging mass 30 while the buoyant member is being pulled downwardly into the water. As the force from the vessel increases, the resultant of the forces in the members connecting the vessel Awith the bottom anchor 56 causes the mass 30 to "be lifted off bot-tom` `and suspended in the water. The weight of the mass 30 oontinues to exert a force attempting to restore the buoyant member to its 'ventical position. This force, coupled with the buoyant force of the member 20, .acts las a damper for sudden increases in the tension ,of the anchor line connecting the ybuoyant member to the vessel and tends to smooth out such sudden increases of .tension and hold the tension in the anchor line within more acceptable working limits.

The mass 30 preferably is made with a large transverse area, such as occurs in a ilat disc, and will react with the water to resist surges or sudden movements of Athe mooring system whiie the mass 30 is lifted oi bottom. This damping 4action of the disc-shaped mass will be eiiective to smooth out yand reduce the amplitude of the movements of the oat member, and hence the movements of the anchor chains to which it is attached, both in the situation where high water has caused the float member to rise sufficiently to lift the mass 30 oi bottom, and in the situation Where there are surges in the tension of the mooring line connecting the iloat member with a vessel.

FIG. 3 illustrates a modilication of a portion or the mooring buoy assembly of this invention, with the same numerals #being used to indicatecomparable elements to those previously described. In this embodiment, the hydrodynamic damping of the oat member is achieved by securing a disc 62 to the element 26. Preferably this disc is secured to the lower end of element 26 and is made with suicient weight to replace the weight of the cement 44 indicated in the previously described embodiment.

The disc 62 may conveniently be lformed with a central opening through Whichthe `element 26 is inserted. A flange 64, which also functions as a water-tight closure member for the lower end of element 26 andas a means for securing the connector member 48 to it, serves to support and position the disc 62 on the element 26. The disc may be secured Iboth to the iiange `and to the element 26 to hold it rigidly in place.

The weighted mass 66 used in lthis embodiment of the invention may be of any convenient form and need not have an expanded area to act yas a hydrodynamic damper, since this function is assumed by the `disc 62. However, in some installations it will be desir-able to employ 'both the disc 62 and -a disc-shaped mass 30 in the salme mooring buoy assembly to provide an increased damping effect over what either of these elements alone Would provide.

These above-described functions of @the mooring assemblage not only tend to smooth out sudden variations 1n the tensions impressed on the interconnected parts, but, as a corollary, tend to smooth tout the resultant variations inthe force applied to the bottom anchor 56 and increase its effective holding power. It is apparent from the foregoing description that the assemblage of lthis invention provides a means for reducing to a marked degree the period of time -when there 1s an appreciable relative movement between :adjacent links of the anchor chains in the dip region where the largest amount of wear occurs in the anchor chains of mooring buoys heretofore employed Vat marine terminals. Since the wear in the anchor chain in the dip region is related to the amount of movement occurring there between the links of the chain, this invention provides a means for reducing the wear in these anchor chains and thus increasing their normal operating life.

It is apparent that modifications may be made to the exempl-ary embodiment of the apparatus described herein without departing from the inventive concept. Therefore, it is intended that the invention embrace all equivalents within the scope of the appended claims.

I claim:

I1. A mooring buoy assembly comprising a substantially cylindrical buoyant member, an elongated rigid element secured at one end to said buoyant member and extending therefrom in coaxial relationship with vthe longitudinal axis thereof, a weight at the other end of said rigid element to maintain said longitudinal axis of said buoyant member disposed vertically when the mooring buoy assembly is installed in a body of water, a length of ranchor chain connected to the said other end of said rigid element, a mass connected to said length of anchor chain, said mass being of sufficient weight to engage the land submerged under said body of water while holding said anchor chain in tension between said mass and said rigid element to submerge the lower portion of said buoyant member in said -body of water la predetermined maximum amount greater than the amount of submergence of said buoyant member when said mass is` not connected to the mooring buoy assembly, the weight of said mass "being selected to prevent said buoyant member from moving vertically upwardly when acted on by upward changes in the eleva-tion of the surface of said water when said changes are below a predetermined maximum elevation above the submerged land and to cause said buoyant member to lift said mass out o-f contact with said submerged land when the amount of submergence of said buoyant member exceeds said predetermined maximum amount, said predetermined maximum amount :occurring when the surface of said water is substantially a-t the elevation of mean higher high water, a second length of anchor chain connected to the first said length of anchor chain,v Ian anchor means connected to said second length of anchor chain and disposable laterally from a position vertically below said buoyant member, and hook means pivotally mounted on the upper end of said buoyant member for attaching a mooring line from a Vessel thereto.

2. A mooring buoy assembly in accordance with claim l wherein said mass is formed with la sufiiciently large transverse area to function effectively as a hydrodynamic damper to resist surging movement of said buoyant member when said mass is lifted off bottom by the buoyant force of said buoyant member.

3. A mooring buoy assembly in accordance with claim l wherein said elongated rigid element is weighted at said other end thereof by a weight affixed to and projecting radially outwardly of said element and -operative -as a hydrodynamic damper to resist surging movement of said buoyant member.

4. A mooring buoy installation comprising a float member located at the surface of a body of water, a weight which engages the submerged land surface, a flexible connecting means connecting said float member to said Weight, the tamount of said weight and the length of said connecting means being :selected to hold said connecting means in tension between said weight and said float member to restrain the bottom portion of said float member submerged in said body of Water below the free-floating position of said float member to hold said float member substantially stationary in elevation with respect lto said submerged land surface when said float member is affected by changes in the elevation 4of said surface of said water within the limits of approximately the elevations oif mean lower low water Xand mean higher high Water, and wherein the said amount of said weight is selected :to cause said float member to lift said weight 0E :of said submerged land surface when the elevation of said surface of said water changes to exceed approximately the elevation of mean higher high water above said submerged land surface, a bottom-engaging anchor means disposed laterally from the position of said weight means son said submerged land surface, a second flexible connecting means `connecting said anchor means to the lower end portion of the `first said flexible connecting means, and means to connect a mooring line from a vessel to said float member.

5. A mooring buoy assembly comprising a float member, a rigid element affixed at one end 4to said float member and extending outwardly therefrom, a weight, a flexible first anchor line means secured to and between the other end of said rigid element and said weight, the amount of said weight and the length of said first anchor line means lbeing selected to place said first anchor line in tension between said weight and said float member to maintain said float member at a substantially consant elevation above a submerged land surface with said weight in contact with said land surace when installed in a body of water while the surface of said water changes in elevation with respect to said submerged land surface between the limits of approximately the elevations of mean lower low water and mean higher high water, but with the amount of said Eweight being such that said weight is lifted by said float member and said first anchor line out of contact with said submerged land surface when said surface of said Water exceeds in elevation lsaid mean higher water, an anchor means laterally displaceable from said first anchor line means, 'a flexible sec-ond anchor line means connecting said anchor means to said first anchor llne means, and means to connect la mooring line from a vessel to said float member.

`6. A mooring buoy assembly comprising a float member, a lthook means pivotally mounted on the upper portion of said float member for detachably connecting a mooring line from a vessel thereto, a length of pipe rigidly afiixcd att its upper end portion to said float member and projecting downwardly from said float member along an axis of symmetry thereof, a weighting material 'disposed within the lower end portion of said length of pipe, a `first anchor chain connected at one end to the lower end of said length of pipe and extending downwardly therefrom, an underwater-bottom-engaging weight element connected to the other end of said first anchor chain, the amount of said weight element and the length of said first anchor chain being selected to hold said rst anchor chain in tension between said weight element and said length of pipe and fwith said weight element having an effective Weight suliicient to prevent said float member from rising and falling with changes in elevation of the surface of a body of water in which a mooring buoy assembly is installed when said changes in elevation occur within approximately the limits of mean lower low water and mean higher high water above the underwater bottom and to be lifted from contact with said underwater bottom when the elevation of said surface exceeds approxiately that of mea-n higher high Water above said runderwater bottom, a `second anchor chain connected at one end to said rst anchor oh'ain at a position adjacent said weight element, a laterally disposed bottom anchor, said second anchor chain connected at its other end to said laterally disposed bottom anchor, said 'weight element beinfg proportioned in Weight to be lifted from contact with `said underwater bottom when a force eX- ceeding a predetermined 'amount is applied fto said hook means isn a direction away from said float member While 10 4 wherein said onderwater-bottom-engaging We-ight ele- 8 ment is constructed with a relatively large transverse 'atea which Vwill react 'with said body of Water to resist vertical movement of said weight element therethrowgh.

References Cited in the file o'f thispatent y UNITED STATES PATENTS v1,958,15135 Elliott -a May l5, 2,856,616 Dodge Oct. 21A, 2,903,716 Zasada e Sept. "1'5, '1959 FOREIGN PATENTS t Y146,774 Great Britain -uty 13, '1929 184,424 Great Britain v Aug. 17, 1922 

1. A MOORING BUOY ASSEMBLY COMPRISING A SUBSTANTIALLY CYLINDRICAL BUOYANT MEMBER, AN ELONGATED RIGID ELEMENT SECURED AT ONE END TO SAID BUOYANT MEMBER AND EXTENDING THEREFROM IN COAXIAL RELATIONSHIP WITH THE LONGITUDINAL AXIS THEREOF, A WEIGHT AT THE OTHER END OF SAID RIGID ELEMENT TO MAINTAIN SAID LONGITUDINAL AXIS OF SAID BUOYANT MEMBER DISPOSED VERTICALLY WHEN THE MOORING BUOY ASSEMBLY IS INSTALLED IN A BODY OF WATER, A LENGTH OF ANCHOR CHAIN CONNECTED TO THE SAID OTHER END OF SAID RIGID ELEMENT, A MASS CONNECTED TO SAID LENGTH OF ANCHOR CHAIN, SAID MASS BEING OF SUFFICIENT WEIGHT TO ENGAGE THE LAND SUBMERGED UNDER SAID BODY OF WATER WHILE HOLDING SAID ANCHOR CHAIN IN TENSION BETWEEN SAID MASS AND SAID RIGID ELEMENT TO SUBMERGE THE LOWER PORTION OF SAID BUOYANT MEMBER IN SAID BODY OF WATER A PREDETERMINED MAXIMUM AMOUNT GREATER THAN THE AMOUNT OF SUBMERGENCE OF SAID BUOYANT MEMBER WHEN SAID MASS IS NOT CONNECTED TO THE MOORING BUOY ASSEMBLY, THE WEIGHT OF SAID MASS BEING SELECTED TO PREVENT SAID BUOYANT MEMBER FROM MOVING VERTICALLY UPWARDLY WHEN ACTED ON BY UPWARD CHANGES IN THE ELEVATION OF THE SURFACE OF SAID WATER WHEN SAID CHANGES ARE BELOW A PREDETERMINED MAXIMUM ELEVATION ABOVE THE SUBMERGED LAND AND TO CAUSE SAID BUOYANT MEMBER TO LIFT SAID MASS OUT OF CONTACT WITH SAID SUBMERGED LAND WHEN THE AMOUNT OF SUBMERGENCE OF SAID BUOYANT MEMBER EXCEEDS SAID PREDETERMINED MAXIMUM AMOUNT, SAID PREDETERMINED MAXIMUM AMOUNT OCCURING WHEN THE SURFACE OF SAID WATER IS SUBSTANTIALLY AT THE ELEVATION OF MEANS HIGHER HIGH WATER, A SECOND LENGTH OF ANCHOR CHAIN CONNECTED TO THE FIRST SAID LENGTH OF ANCHOR CHAIN, AN ANCHOR MEANS CONNECTED TO SAID SECOND LENGTH OF ANCHOR CHAIN AND DISPOSABLE LATERALLY FROM A POSITION VERTICALLY BELOW SAID BUOYANT MEMBER, AND HOOK MEANS PIVOTALLY MOUNTED ON THE UPPER END OF SAID BUOYANT MEMBER FOR ATTACHING A MOORING LINE FROM A VESSEL THERETO. 